The present invention generally relates to the measurement of tissue and other materials, often so as to diagnose vulnerable plaque, colon cancer, and other diseases of tissues adjacent body lumens or the skin. Embodiments of the invention may employ insertable probes utilizing magnetic resonance imaging (MRI) and/or nuclear magnetic resonance (NMR) phenomena.
Many diseases exist that can be successfully treated if diagnosed in a timely manner. Examples of such life threatening diseases that can be successfully treated include atherosclerosis and cancer. A variety of diagnostic imaging modalities have been developed to help diagnose these and other diseases including ultrasound, angiography, optical coherence tomography (OCT), thermography, spectroscopy, and MRI. Unfortunately, current techniques and apparatus used to diagnose diseases are often less than ideal, in some instances being ineffective and/or too complex or costly to implement on a routine clinical basis. Failures and delays in diagnosing life threatening diseases such as cancer and atherosclerosis can lead to morbidity and/or mortality.
Atherosclerosis, a hardening and/or thickening of the arteries, is a leading cause of mortality and morbidity in the United States. Atherosclerosis is a progressive pathological process, often involving the slow buildup of fatty substances, cholesterol, cellular waste products, calcium, and fibrin in the arterial wall that can lead to blockage of the artery, and that can be a factor in multiple conditions including coronary heart disease, myocardial infarction, angina pectoris, cerebral vascular disease, thrombotic stroke, transient ischemic attacks, organ damage, vascular complications of diabetes, and/or the like.
Interventional treatments of standard plaques include coronary artery bypass surgery, percutaneous transluminal angioplasty, and stenting, with these therapies generally being targeted at hemodynamically significant stenoses identified by conventional x-ray angiography. These treatments are often quite effective in treating standard calcified and other stenotic plaques, and drug-eluting stents may extend the benefits within the coronary arteries. However, the materials and potential effects of plaques may vary between different patients, and even between different lesions of a single patient. Some plaques, and particularly those referred to as “vulnerable plaque” (which may be characterized by one or more particular materials or structural forms) may play a disproportionate role in acute coronary syndromes and sudden heart attacks.
The components of vulnerable plaques may include a soft or even liquid lipid-rich substance and a hard, collagen-rich tissue cap. In postmortem studies, vulnerable plaques may be characterized by a thin (in some cases less than 65 microns) fibrous cap, a large lipid-rich pool, and increased macrophage activity. Treatments appropriate for standard stenotic plaques may be undesirable for such lesions, as a disruption of the fibrous cap integrity in these rupture-prone plaques may release procoagulant factors, resulting in thrombus formation and the potential for an acute coronary event. Therefore, practical diagnostic techniques able to distinguish vulnerable, high-risk, rupture-prone plaque from low-risk, calcified plaques could prove very valuable in evaluation and treatment of atherosclerosis-related cardiovascular disease. As known techniques for characterizing plaques have not yet gained wide acceptance, a need exists for new and improved techniques to identify and diagnose patients with vulnerable plaque.
Colon cancer is also a major cause of death, and can affect the population at a relatively early age. Colon cancer can be successfully treated, and both diagnosis and treatment are available. Nevertheless, for a number of reasons, colon cancer continues to take lives. In some cases, this may be related to inadequacy of known colonoscopy techniques in identifying cancerous lesions. While cancerous polyps may be anatomically distinct, some cancers can manifest themselves as a thickening of the colon wall, which can be difficult to evaluate. Therefore a need exists for an improved probe that can be used in conjunction with colonoscopy to resolve these ambiguous cases, potentially resulting in improved diagnostic efficacy.
There are still other clinical applications where there exists a need to examine suspicious areas identified during examination with visible light. These include broncoscopy, urethral, esophageal and skin examinations, and the like.
While MRI has shown promise for the diagnosis of diseases, current NMR systems and images have limitations that have limited the application of these techniques. In particular, standard NMR images of small and/or internal tissue structures may have a resolution which is less than ideal for detecting and diagnosing fine tissue structures implicated with many diseases, including the fibrous cap of atherosclerotic plaque and the thicker colon walls that can be associated with colon cancer. Also, current MRI systems can be costly and bulky, and a patient scan can take several minutes.
While known MRI systems have allowed a large number of patients to benefit from diagnostic imaging, still further improvements would be desirable. For example, it would be advantageous to provide smaller MRI systems that are compatible with existing diagnostic equipment. Decreased patient scan time would also be desirable and help to integrate MRI with current diagnostic tests. It would also be advantageous to more effectively diagnose diseases, for example with high resolution MRI images. At least some of these potential advantages may be realized by the systems, devices, and methods described herein below.